Generic Filters; Creating Filters Overview; Creating Filters Using Command Line Interface; Filter File Components In Cli - 3Com OfficeConnect Remote 812 Cli User's Manual

6-28 C 6: M
HAPTER ANUAL

Generic Filters

Creating Filters
Overview
Creating Filters Using
Command Line
Interface
Filter File Components in
S
ETUP
Generic filters are protocol-independent and are specified by byte and offset
values in a packet. Packets are filtered by comparing each packet's offset value
and byte information with the values that you define in the filter. The router will
accept or reject the packet based on the result.
Creating generic filters can be a complex task. Only experienced users should
employ generic filters, and strictly in cases where data and advertising filters
cannot provide the filtering capabilities that you require.
Filters can be set one of two ways in the OfficeConnect Remote 812: Using CLI or
using the OfficeConnect Remote 812 Manager.
The more flexible way of setting filters is through the Command Line Interface
(CLI). Both data and advertisement filters can be set using CLI. For more
information on accessing CLI, refer to the OfficeConnect Remote 812 ADSL
Router CLI User's Guide.
Data Filters can be set using the HTML Manager (the OfficeConnect Remote 812
Manager). Data filters are used to remove packets from the normal flow of data
traffic. They can be applied to IP, IPX, and/or Bridge traffic. Advertisement filters
are used to restrict information in outgoing or incoming advertisement packets,
i.e. IP RIP, IPX RIP, and IPX SAP packets.
Before creating a filter file, you should carefully identify the information you want
to filter. Decide if you want a filter that discards packets (such as reject all IP
packets whose IP source address is 192.168.200.50) or accept only a subset of
packets (such as accept only bridged packets if the destination MAC address is
002069000001 or 002069000002). Also determine where you want to place the
filter. For example, figure out if you want to apply the filter to packets coming into
the Ethernet port, to packets going out the WAN (ATM) port, or to packets
coming from a specific VC/remote site.
The first step in creating a filter on the OfficeConnect Remote 812 is to create a
file using a text editor on a workstation. The file will contain filters defined in the
OfficeConnect Remote 812 filter syntax (described below). File names should be
short and descriptive, such as IP.FLT.
The next step is to use TFTP (Trivial File Transfer Protocol) to copy the filter file from
the workstation to the OfficeConnect Remote 812.
You then use CLI commands to add the filter file to the list of filters and apply the
filter to the appropriate interface or VC / remote site profile.
You define the filtering rules used by the router within filter files. Filter files are
CLI text files that are stored in the unit's FLASH memory. You can create and modify
filter files using an off-line text editor, then TFTPing the finished file on to the unit.
To be valid, a filter file must always have the following file descriptor on the first
line: #filter
Be sure that no blank space precedes the descriptor, or an error will occur.